Determination of pore size distribution of reservoir rock

Abstract

This disclosure provides a method of determining a pore throat size distribution of reservoir rock, comprising injecting a set of different-sized probe particles through a portion of reservoir rock and measuring retention volumes or times of each of the different-sized probe particles eluting from the portion of reservoir rock. This disclosure also provides a testing apparatus comprising a probe tube for receiving a set of different-sized probe particles in an elution fluid returning from a portion of reservoir rock and an analytical module connected to receive the elution fluid from the probe tube. The module includes a flow cell to receive the elution fluid from the probe tube, a radiation source positioned to direct a radiation beam though a window of the cell into the eluting fluid in the cell, and a sensor for detecting portions of the radiation beam that have interacted with the different-sized probe particles such that retention volumes or times each of the probe particles of one size class can be distinguished from all other size classes of the set.

What is claimed is: 
     
       1. A method of determining a pore throat size distribution of reservoir rock, the method comprising:
 injecting a set of different-sized probe particles through a portion of reservoir rock, the injecting includes pumping the probe particles through a probe tube that interfaces with the portion of reservoir rock that is located in a below-ground rock formation; 
 measuring retention volumes or retention times of each of the different-sized probe particles eluting from the portion of reservoir rock, the measuring includes reversing a direction of the injection flow and measuring the time or volume for the probe particles to elute back into the probe tube; and 
 calculating the pore throat size distribution of the reservoir rock based on the retention volumes or the retention times measured for the different-sized probe particles using inverse size exclusion chromatography. 
 
     
     
       2. The method of  claim 1 , wherein the injecting includes pumping the probe particles through the portion of reservoir rock at a constant flow rate and the measuring includes measuring the retention times of the probe particles eluting from the portion of reservoir rock. 
     
     
       3. The method of  claim 1 , wherein the injecting includes pumping the probe particles through the portion of reservoir rock at a constant flow pressure and the measuring includes measuring the retention volumes of the probe particles eluting from the portion of reservoir rock. 
     
     
       4. The method of  claim 1 , wherein the injecting includes sequentially pumping the different-sized probe particles into the portion of reservoir rock from a smallest particle size to a largest particle size. 
     
     
       5. The method of  claim 1 , wherein the portion of reservoir rock is an above-ground sample from a below-ground rock formation. 
     
     
       6. The method of  claim 1 , wherein the portion of reservoir rock is part of a below-ground rock formation. 
     
     
       7. The method of  claim 1 , further including providing an injection fluid containing the set of probe particles by mixing the set probe particles with a pre-injection fluid, wherein the set probe particles are injected into the portion of reservoir rock as part of the injection fluid. 
     
     
       8. The method of  claim 7 , wherein providing the injection fluid includes filtering a portion of drilling fluid to provide at least a portion of the pre-injection fluid. 
     
     
       9. A method of determining a pore throat size distribution of reservoir rock, the method comprising
 injecting a set of different-sized probe particles through a portion of reservoir rock, the injecting includes pumping the probe particles through a first probe tube that interfaces with the portion of reservoir rock that is located in a below-ground rock formation; 
 measuring retention volumes or retention times of each of the different-sized probe particles eluting from the portion of reservoir rock, the measuring includes measuring the time or volume for the probe particles to elute into a second probe tube that is separated from the first tube and interfaces with the portion of reservoir rock; and 
 calculating the pore throat size distribution of the reservoir rock based on the retention volumes or the retention times measured for the different-sized probe particles using inverse size exclusion chromatography. 
 
     
     
       10. The method of  claim 9 , further including:
 reversing a pump flow such that fluid that has eluted into the second probe tube is flowed back through the second probe tube and into the portion of reservoir rock; and 
 measuring the time or volume for the probe particles to elute back into the first probe tube. 
 
     
     
       11. A testing apparatus for determining a pore throat size distribution of reservoir rock, the apparatus comprising:
 a probe tube for receiving a set of different-sized probe particles in an elution fluid returning from a portion of reservoir rock; and 
 an analytical module connected to receive the elution fluid from the probe tube, the analytical module including:
 a flow cell to receive the elution fluid from the probe tube; 
 a radiation source positioned to direct a radiation beam though a window of the cell into the eluting fluid in the cell; and 
 a sensor for detecting portions of the radiation beam that have interacted with the different-sized probe particles such that retention volumes or times each of the different-sized probe particles of one size class can be distinguished from all other size classes of the set. 
 
 
     
     
       12. The apparatus of  claim 11 , wherein the radiation source is configured to direct the radiation beam at a wavelength that causes different photo-luminescent groups of different-sized probe particles in each of the size classes to fluoresce light at different wavelengths. 
     
     
       13. The apparatus of  claim 11 , wherein the different-sized probe particles in each of the classes have different refractive indexes that cause unique refractance of the radiation beam to refract the portions of the radiation beam at different wavelengths. 
     
     
       14. The apparatus of  claim 11 , wherein the different-sized probe particles in each of the size classes have different light scattering characteristics that cause unique light scattering of the radiation beam to refract the portions of the radiation beam at different wavelengths. 
     
     
       15. The apparatus of  claim 11 , wherein the set of different-sized probe particles range in size corresponding to a root mean diameter ranging from about 0.1 microns to 100 microns. 
     
     
       16. The apparatus of  claim 11 , wherein the set of different-sized probe particles are in an injection fluid held in one or more storage containers of the apparatus, the one or more storage containers coupled to an injection pump configured to inject the injection fluid through the portion of reservoir rock. 
     
     
       17. The apparatus of  claim 11 , further including a filter having size cut-off that is less than a smallest-sized one of the different-sized probe particles of the set, the filter configured to filter a portion of drilling fluid allowed to enter through a port of the apparatus, wherein a filtered portion of the drilling fluid is included as part of the injection fluid. 
     
     
       18. The apparatus of  claim 11 , further including a second probe tube, the second probe tube configured to deliver an injection fluid with the set of different-sized probe particles to the portion of reservoir rock. 
     
     
       19. The apparatus of  claim 11 , further including a second one of the analytical module connected to a second probe tube, the second analytical module configured to receive a back flow of the injection fluid and the elution fluid.